Industrial strength fabrics and materials have many outdoors applications, such as covers for football or baseball fields, covers for tennis courts, walls or fences, and liners and covers for ponds and reservoirs. Since these industrial fabrics are often used to cover or line large surface areas, several panels of fabric may have to be joined together in order to facilitate installation. Therefore, a seaming or welding together of the fabric panels is often done at the site location, as the liner or cover is installed.
When the panels of fabric are to be used under stress conditions such as outdoors, in high winds and rain, for example, the strength of the fabric liner or cover is dependent on the weakest seam. If panels of a class of industrial fabrics known as liquid impervious, flexible membranes are used to line or cover ponds or reservoirs, for example, various environmental conditions such as pond irregularities, settling and cracking, high winds, rain and ice may cause the fabric to split, especially at its weakest seam. Therefore, it is necessary to provide not only air and watertightness, but also a structurally strong and sound mechanical seam for joining panels of industrial fabric.
In the installation of industrial fabric liners or covers, there are also other considerations, such as the contours of the surface to be lined or covered. For example, it may be desirable to cover a flat football or baseball field with a watertight cover having seams lying flat on the ground so that water will not collect between panels of the cover when it rains. Other examples are liners for basin-shaped, waste-holding ponds or pits, in which basin-shaped liners might be used to contain seepage of waste products from the pond or pit into the soil, where watertight seams are essentially underwater. Airtight seams might be necessary if industrial fabric covers are used to cover and trap gas over fermentation piles or collection ponds. Thus, there should be a versatility in seam formation so that any of many different configurations may be accommodated.
Present seams or welds, which provide both strength and watertightness and which are made in the field, normally require adhesives or gum tape. For thermoplastic fabrics, hand-held portable heat welders may also be used. The problem with seaming or welding fabric panels together with adhesives or gum tape is that these methods are time-consuming and may be unreliable depending on the skills of the installer. The quality of these seams may also be dependent on temperature or weather conditions. These seams cannot always be made in extremely hot, cold or wet weather. Also adhesive seams require curing and drying time before a good bond strength is developed and the seams are sufficient for testing and use. Thus, with conventional techniques, it may not be possible to install a liner quickly enough to contain water leaking through an earthen dam, for example.
For thermoplastic fabrics, the hand-held heat welding method for making seams has advantages over adhesive seams. However, it cannot be used with non-thermoplastic industrial fabrics. Thus, if thermoplastic fabric is not the fabric of choice for a particular job, this method is not available.